Most Helpful Guy
I hear your concerns...
You really have to think about how much you trust him. A little or a lot.
If it is a little then decline the invitation just say you don't feel comfortable with so many guys around and/or get some girlfriends to join you.
If you trust him a lot then you have nothing to worry about. But really figure out how much. If there is any doubt then you might want to bring some friends along. Strength in Numbers!!!
Ultimatly this is a tricky one to answer. It really comes down to trust and gut reaction. If you still want to go but have a slight doubt bring some friends and hopefully that will help.
Most Helpful Girl
You right to be concerned. 2 & 1/2 weeks is awful soon in my books. I would be cautious if I were you.